Infant formula is used as a supplement to or substitute for breast milk when a mother cannot or does not want to breast feed her infant. Ideally, the composition of the infant formula would be exactly the same as the composition of human milk. Nonetheless, because infant formulas are typically made with cow milk (and sometimes soy protein), on a molecular level, these formulas are not the same as human milk. Nonetheless, infant formulas are designed to mimic the formulation of human milk as much as possible. Furthermore, infant formulas should contain nutrients as listed by the U.S. Code of Federal Regulations, 21 CFR 107.100, 1998, as presented in Table 1. The resultant infant formulas can be called "humanized milk", "simulated human milk", "simulated mother milk", "simulated breast milk" and "infant nutritional formula".
An infant formula which contains all the essential macronutrients and micronutrients, have heretofore been available only in shelf-stable sterilized products. Sterilized products are generally sold in hermetically sealed containers such as cans and are intended to have a long room temperature shelf-life. Table 2 lists several commercially available shelf-stable sterilized infant formulas. Such formulas require expensive processing steps which must be carefully controlled to properly remove microorganisms and bacterial enzymes. As will be discussed further herein, sterilization processes, due to the severity of the heat treatment can cause undesirable physical, chemical, enzymatic and microbial changes which deleteriously affect the final product.
Moreover, although such sterilized products are often marketed as "ready-to-feed" (RTF), they are typically stored at room temperature, and enzymatic reactions still occur, albeit slower, during room temperature storage of sterilized products. Such reactions can result in a host of undesirable defects, such as the destruction of vitamins which are necessary to the integrity of the overall product. Since sterilized products are designed to have up to one and a half (11/2) year of room temperature shelf-life, such products will have a different actual content of degradable micro nutrients (vitamins) in the early part of its shelf-life as compared to the latter part. Thus, an infant will obtain a different and unknown amount of vitamins depending on when the sterilized product is consumed.
To account for this degradative process during long-term shelf-life, manufacturers of sterilized infant formulas often include up to 50% to 70% more of a given vitamin than would normally be included to account for the inherent degradation loss and to ensure the product is likely to contain at least the labeled amount of nutrients at the end of its shelf-life. Such large overdosing results in an imbalance in the taste of the product, particularly if consumed in the early stages of its shelf-life. Moreover, the cost factor of including such large overdoses is considerable. In addition to the high cost of sterilization, and increased overdosing of vitamins, sterilization processes require high cost packaging, such as in metal cans.
Like milk, liquid infant formulas (usually containing milk proteins and sometimes soy protein) are heated for a variety of reasons, the main reasons being: to remove potential pathogenic organisms and to increase shelf-life. The major concerns about the resulting products of thermal process are safety and quality. Like milk, heat-treated infant formulas should not be a public health risk. They should have a good keeping quality, provide an intended balance of nutrients, and be of desirable sensory characteristics, i.e., appearance, color, flavor, and mouth feel. When milk or infant formulas are heated at a constant temperature, all their constituents and components will be affected, but to different extents. Increasing the temperature will accelerate reaction rates. But different reactions will be affected to different extents. Physical, chemical, enzymatic and microbial changes will depend principally upon the time-temperature conditions, but will also be influenced by other factors, such as composition, pH, and oxygen content. The wide range of reactions taking place when infant formulas are heated will influence the safety and quality of the product. Upon heating of products at higher temperatures for longer times, some undesirable changes can also take place (e.g., decrease in pH, Maillard browning, cooked caramel flavor, denaturation of whey proteins and interaction with casein). The changes that take place during heating and subsequent storage, can affect the nutritional value and sensory characteristics.
In thermal processing, the most important parameter is the level of microbial inactivation achieved. For safety reasons, the minimum holding time (residence time) should be considered for microbial inactivation, although this will give an underestimate of the true level of microbial inactivation.
In terms of microbial quality and reducing spoilage rates, the emphasis is toward that of prevention. One approach, now widely used, is that of Hazard Analysis Critical Control Points (HACCP). Here the philosophy is to identify where hazard may occur from raw materials, different processing stages, packaging, or subsequent handling and storage. Critical control points are then established. These are points in the production process where the hazard can be effectively controlled. Loss of control permits the realization of the potential hazard as an unacceptable food safety or spoilage risk.
The quality of raw materials (ingredients) also has a pronounced effect on the quality of the final product. From the microbial point of view, the ingredients must be free of serious pathogens, and have initial total bacterial counts not more than 104 per gram. This reflects good hygiene in production of the ingredients. It is also useful to monitor psychotropic bacteria in raw ingredients (via direct assay of proteolytic enzymes) as they are usually predominant among the microorganisms found in pasteurized products.
Sterilization (Prior Art)
The currently practiced process for preparation of infant formulas is thermal sterilization. Table 2 shows that, at the present time, there are more than a dozen of these liquid infant formulas available in the market. Typically, these products are commercially sterile and offered in metal cans or heavy plastic containers and are stored at room temperature (i.e., they are shelf-stable). None of these infant formulas are prepared or offered as ultra-pasteurized or pasteurized product.
Sterilizing a product means exposing it to such powerful heat treatment that all microorganisms are killed. However, absolute sterility is not possible. The term "Commercial Sterility" is used instead. From the U.S. regulations point-of-view (21 CFR 113.3, 1998), "Commercial Sterility" of thermally processed food means the condition achieved
1) By the application of heat which renders the food free of PA1 2) By the control of water activity and the application of heat, which renders the food free of microorganisms capable of reproducing in the food under normal non-refrigerated conditions of storage and distribution.
(a) Microorganisms capable of reproducing in the food under normal non-refrigerated conditions of storage and distribution; and PA2 (b) Viable microorganisms (including spores) of public health significance; or
It is common practice in the commercial sterilization of low-acid foods (i.e., pH&gt;4.5) to achieve at least a 12 decimal reduction for spores of Clostridium botulinum, because they are the most heat resistant of the major food poisoning organisms.
Two main methods are used for sterilizing liquid infant formulas: in-container sterilization, and UHT (Ultra High Temperature) treatment. For in-container sterilization, two different types of sterilizers are used: autoclaves (retorts) for batch processing, and hydrostatic towers for continuous processing. For UHT treatment, where the product is sterilized in a continuous flow followed by aseptic filling, two different types of sterilizing systems are also used. One of these methods operates on the principle of direct steam injection or steam infusion and the other on indirect heating in heat exchanger.
In the retort sterilization method, the infant formula is usually preheated and then filled into a clean can, hermetically sealed, and placed in a steam chamber and sterilized, normally at 121.degree. C. (250.degree. F.) for 15-40 minutes. The batch is then cooled and the retort filled with a new batch. The fact that sterilization takes place after filling eliminates the need for aseptic handling but, on the other hand, only heat resistant packaging materials can be used. In the hydrostatic tower method of in-container sterilization, the infant formula containers are slowly conveyed through successive heating and cooling zones in the sterilizer. These zones are dimensioned to correspond to the required temperatures and holding times in the various treatment stages.
In the UHT treatment, the infant formula is pumped through a closed system. On the way it is preheated, sterilized, homogenized, cooled, and filled aseptically. This method is generally understood as a treatment in which product is heated to a temperature of 135 to 150.degree. C. in continuous flow in a heat exchanger for a sufficient length of time to achieve commercial sterility with an acceptable amount of change in the product. From the U.S. regulations point-of-view (21 CFR 113.3, 1998), aseptic processing and packaging means the filling of a commercially sterilized cooled product into pre-sterilized containers, followed by aseptic hermetical sealing, with a pre-sterilized closure, in an atmosphere free of microorganisms. Sterilization takes place at 135-150.degree. C. (275-300.degree. F.) for 2-5 seconds, either by means of indirect heating, direct steam injection or infusion. All parts of the system downstream of the actual sterilization section are of aseptic design in order to eliminate the risk of reinfection.
Although bacterial enzymes do not normally survive an in-container process to cause adverse effects during subsequent storage of the product, they will survive a UHT process to a high degree to give such problems as off-flavor and gelation during storage. In the absence of some other system for inactivating the enzyme, e.g., the low temperature holding system (such as for ultra-pasteurized or pasteurized products), the only solution is to avoid these enzymes by careful control of the raw material to prevent the growth of the psychotropic organisms which give rise to these very resistant enzymes.
Aseptic filling is an integral part and a crucial step in UHT treatment. The container itself will need sterilization before filling. Cans are typically sterilized by superheated steam. Presently, most sterilized infant formulas in the market are packaged in cans.
Most packages used in the UHT processes are sterilized with hydrogen peroxide at a concentration of between 20 and 35 percent and a temperature between 80 and 85.degree. C. Residence times of several seconds are required. Care should be taken to ensure that all hydrogen peroxide is removed, as it is a strong oxidizing agent. The oxygen permeability of the plastic is important and may well influence the shelf-life of the product.
Another term used in connection with ULHT treatment to characterize the quality of the treatment is the "shelf-life" of the product. This is defined as the time which the product can be stored without the quality falling below a certain acceptable, minimum level. The concept is subjective--the shelf-life can be very long if the criteria of product quality are low. The physical and chemical limiting factors of shelf-life are gelling, increase of viscosity, sedimentation, and phase separation. The organoleptic limiting factors are deterioration of taste, smell, and color.
There is a need for a refrigerated ready-to-feed or concentrated infant formulas that do not suffer from the disadvantages of sterilized products. Such infant formulas should include all the required nutrients as listed in Table 1, should be organoleptically pleasing, have a shelf-life of between about 1 and 16 weeks and use the simple and inexpensive processing of pasteurization or ultra-pasteurization. Moreover, there is a need for cost effective ready-to-feed and concentrated infant formula which can be refrigeration-stored in inexpensive packaging, such as gable top cartons or plastic containers traditionally used in milk products.
The present invention meets these and other needs, as will come apparent in the description provided below.